Microphone in a cylindrical housing having elliptical end faces

ABSTRACT

The device is now a squarely-truncated horizontal cylinder capped at each end by a circular disc central to which is placed a transducer. With amplification the device yields the sound spectrum which can be heard in consciousness. The cylinder is extended just sufficiently to accommodate truncation at 35 degrees 16 minutes yielding a chiral pair of elliptical openings which, with amplification, add cues to sound-source localization and range determination which are not heard but are known subconsciously. The long axes of the elliptical openings are set orthogonally at 45 degrees to the horizon, thus allowing correct spatial orientation. Elliptical caps, with open edges, are applied to the elliptical ends of the device hiding the transducers from view and from direct sound. To cancel internally generated resonances the enclosed spaces are filled with fine irregularly-shaped particulate matter.

The present invention relates to a precision microphone and to certainderivative applications of the microphone, particularly in the form ofhearing aids.

BACKGROUND OF THE INVENTION

The applicant's Canadian patent no: 2,076,288, discloses a microphonefor recording sounds, including directional and range information in thesounds.

The present invention incorporates certain improvements in themicrophone design and applies the microphone to hearing devices,especially for the hearing-impaired.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided amicrophone comprising:

a hollow cylindrical housing with a lateral axis, and having twonon-parallel elliptical end faces oriented mirror symmetrically withrespect to a plane perpendicular to the lateral axis;

two circular transducer mounting plates extending across the housing,adjacent the respective end faces, substantially perpendicular to thelateral axis;

two microphone transducers mounted centrally in respective ones of thetransducer mounting plates for receiving sound from outside thetransducer mounting plates;

end panels of air-pervious material extending across and closing therespective end faces;

two sound damping tragus pads secured to inner faces of respective onesof the end panels, each tragus pad having an elliptical periphery spacedfrom the housing.

end panels of an air-pervious material extending across and closing therespective end faces;

The microphone, in its preferred form, is referred to herein as the‘precision microphone’.

In use, the precision microphone is normally positioned with the lateralaxis horizontal and the long axes of the two elliptical end facesconverging downwardly to a front side of the microphone to meet at adihedral angle of 70 degrees 32 minutes. These end faces are identifiedas ‘right’ and ‘left’ end faces.

This arrangement, through the use of a circular transducer mountingplate and an elliptical sound access to the microphone provides ananalog to the elliptical to circular transition that is found in thehuman hearing system.

The outer circumferential edge of each mounting plate is preferablytangent to the inner circumferential edge of the adjacent end face ofthe housing, at the point where the axial distance between the end facesis a minimum.

The tragus pad provides a functional analog to the external ear of thehuman hearing system and serves to damp predominantly left-rightmid-frequency sound information arriving at the microphone along thelateral axis where the transducer sensitivity is greatest. This yields abetter balance of all the sound information.

These modifications correct certain anomalies that have been observedwhen recording under particular conditions with the prior design.

The currently preferred tragus pad comprises two air-imperviousmembranes secured together along the elliptical periphery, a stiffeningmaterial between the membranes, and a viscous fluid in the space betweenthe membranes. It also includes a small circular port on the lateralaxis.

A particulate material may fill the housing between each transducermounting plate and the adjacent tragus pad to obviate distortion due toreflection in this part of the housing. The preferred particulatematerial is a sound damping material, for example powdered cork. It maybe is coated with a viscous liquid, for example mineral oil.

The microphone may be ported by an aperture communicating the interiorof the housing between the transducer mounting plates with the exteriorof the housing. This is desirably a slit extending along the housing,between the mounting plates at the shortest length of the housing. Thisrenders the housing, otherwise a column subject to resonance, aperiodic.A sound damping material, preferably a particulate material, for exampleoiled, crushed cork, preferably fills the housing between the end platesto damp other resonances.

The benefits of using directional microphones in hearing aids are known.Reference may be made, for example to Killion et al. U.S. Pat. No.6,567,526 and the literature referenced in that patent. The microphoneof the present invention may be adapted to this purpose for eitherexternal or in-the-ear applications.

Thus, according to another aspect of the present invention there isprovided a hearing aid comprising;

a cylindrical housing with a lateral axis and having non-parallelelliptical end faces oriented mirror-symmetrically with respect to aplane perpendicular to the lateral axis;

two microphone transducers mounted in the housing to receive sound fromthe respective end faces;

a housing mount for mounting the housing on an eyeglass frame such thatwhen worn, the lateral axis is substantially horizontal and theelliptical end faces converge forwardly and downwardly;

amplifiers coupled to the respective microphone transducers forreceiving transducer signals therefrom;

ear pieces including respective earphone transducers connected to theamplifiers for receiving amplified transducer signals and converting thesignals into sounds.

This provides a hearing aid incorporating an embodiment of themicrophone that may be mounted on a frame for eyeglasses in order toreceive and transmit to the wearer not only the ambient sounds but alsothe directional and range information contained within the ambient soundfield so as to improve the signal to noise discrimination of the hearingaid.

According to a third aspect of the present invention there is provided ahearing aid comprising:

a cylindrical housing with a lateral axis and an elliptical end face;

a microphone transducer mounted in the housing to receive sound from theelliptical end face;

an amplifier for receiving electrical signals from the microphonetransducer and amplifying the signals;

an earphone transducer for receiving amplified signals from theamplifier and converting the amplified signals into sound waves;

an earpiece for mounting the housing on a human ear with the lateralaxis substantially horizontal and long axis of the elliptical end facesloping downwardly to the front.

According to this aspect, for the hearing assist is divided and may belocated on or adjacent to the lateral zero axis of the human head, thusproviding a more accurate representation of the surrounding sound field.This aspect of the invention is particularly suited for use as anin-the-ear hearing aid.

Another aspect of the invention is an improved loudspeaker system,referred to herein as the ‘precision loudspeaker’.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate exemplary embodiments ofthe present invention:

FIG. 1 is an elevation, partly in cross section, of a microphoneaccording to the present invention.

FIG. 2 is a top view of the microphone.

FIG. 3 is an end view of the microphone.

FIG. 4 is an end view like FIG. 2 showing the tragus pad in broken line

FIG. 5 is a broken away view of the tragus pad, showing the internalstructure.

FIG. 6 is a section along line 6-6 of FIG. 5.

FIG. 7 is an isometric view of an embodiment of hearing assist mountedon an eyeglass frame.

FIG. 8 is a front elevation of a second embodiment of hearing assist.

FIG. 9 is a top view of the second embodiment of hearing assist.

FIG. 10 is a front elevation of a modified loudspeaker system.

DETAILED DESCRIPTION

Referring to the accompanying drawings, and particularly to FIGS. 1through 6, there is illustrated a microphone 10 having a housing 12supported by a standard 14 on a base 16. The base is equipped with aspirit level 18 so that the microphone can be properly leveled for use.

The microphone housing has a cylindrical sidewall 20 with a longitudinalaxis X-X and elliptical ends 24 that slope downwardly and inwardlytowards the front in planes oriented at 35° 16′ to the longitudinal axisto intersect at the dihedral angle of a regular tetrahedron (70° 32′).The long axis of each end face is oriented at an angle of 45° to thehorizontal.

At each end of the housing is a transducer mounting plate 26 extendingacross the housing perpendicular to the axis X-X. The outer face of themounting plate is flush with the innermost point on the end 24.

Each mounting plate 26 has a central bore 28 accommodating a microphonetransducer 30. The electric leads 32 from the transducer run through thestandard 14 into the base 16.

The microphone housing is covered with an appropriate fabric material 34that is acoustically transparent, at least where it covers the open endsof the housing.

Secured to the inner face of the fabric covering where it extends acrossthe housing end is a sound damping tragus pad 40 (FIGS. 4, 5 and 6)having an elliptical periphery 42 spaced from the inner surface of thehousing side wall, leaving an unobstructed elliptical gap 44 around thetragus pad. The chamber between the tragus pad 40 and the mounting plate26 is filled with a particulate sound damping material 46, for exampleground cork, which is coated with a viscous liquid, for example mineraloil.

FIGS. 5 and 6 illustrate the construction of an exemplary tragus pad.The pad has an envelope formed from two membranes 48 of garden clothsecured together along the elliptical periphery 42. A stiffeningmaterial 50 is placed between the membranes. In this exemplaryembodiment this is a stiff net or mesh. A viscous fluid 52, in thisembodiment mineral oil fills the space between the membranes. The traguspad has a small circular through port 54 on the lateral axis X-X of thehousing.

To prevent resonance within the housing 12, the hollow center of thehousing is ported by an aperture comprising a horizontal slit 56extending from end to end of the housing, at the position of shortestaxial length, and ending just inside the mounting plates 26. Between theend plates 26, the housing is filled with oiled, crushed cork 57 to dampother resonances.

FIG. 7 illustrates an embodiment of the microphone applied in anexternal hearing assist or aid. This microphone 58 is a miniaturizedversion of that described above, with an internal, two channel amplifier60. The housing carries a mounting clip 62 for mounting the microphoneon an eyeglass frame 64 such that when worn, and with the wearer's headupright with the eyes focussed on the horizon, the lateral axis of themicrophone housing is substantially horizontal and the elliptical endfaces converge forwardly and downwardly. The left and right outputs fromthe amplifier are connected to the earphone transducers of respectivebud earpieces 66 to deliver amplified sound, including the desireddirectional and range information to the user.

FIGS. 8 and 9 illustrate another embodiment of the microphone applied asan in-the-ear hearing assist or aid. In this case, the microphone isphysically separated into right and left hand elements 68 and 70respectively, that are allochiral or mirror-symmetrical. Each componenthas an earpiece 72 moulded to fit the ear of a user. The microphoneelement is embedded in the earpiece along with an amplifier 74 and anearphone transducer 76. The microphone element has a cylindrical housing78 and is constructed in the same way as one end of the microphone ofFIGS. 1 through 4. The microphone transducer is the input source to theamplifier 74 which drives the earphone transducer 76. When worn, theaxis of each component is at least generally aligned with the lateral,horizontal tilt axis Y-Y of the head, to pass through the “zero point”79 where the tilt axis intersects the vertical rotation axis Z-Z of thehead.

FIG. 10 illustrates a loudspeaker and components of the loudspeakerintended for use in reproducing sound recorded using the microphone 10.The loudspeaker 80 has a center unit 82, a left end unit 84 and rightend unit 86. The three units are all configured and arranged asdescribed in the applicant's Canadian patent 2,076,288. In this system,two additional components 88 and 90 are added at opposite ends. Each ofthe additional components includes a speaker enclosure 92 housing a lowto mid-range speaker 94, radiating outwardly (see “O. SOUND ENVELOPES”in “THEORETICAL CONSIDERATIONS” (infra)). The enclosure is ported byports 96 on the bottom below. The additional left and right speakers aredriven by left and right amplifier outputs respectively through acrossover 98 operating at approximately 400 Hz.

The enclosures 86 are filled with light weight, fractal-like bodies,e.g. oiled popcorn to render the enclosures aperiodic to eliminatecolour.

Theoretical Considerations

In consideration of and further to the theoretical considerationspresented in the applicant's Canadian patents 1,060,350, issued 14 Aug.1979; 1,282,711, issued 9 Apr. 1991; and 2,076,288, issued 30 Jan. 2001(U.S. Pat. Nos. 4,122,910; 4,591,343 and 5,666,433) the entiredisclosures of which are incorporated herein by reference, the followingconsiderations form the basis of the further developments described andclaimed herein:

A. Towards a Tetrahedral Theory of Sound Source Localization and RangeDetermination

The following postulates are the basis of the current theory on whichthe present invention is based:

1. Sound source localization is an active process whereby human cochleaesimultaneously encode sound source identification, range andlocalization information.

2. In free field situations, evoked otoacoustic emissions yield bands orcurves which comprise a primary band relevant to sound sourceidentification and range determination together with secondary sidebandsof slightly higher and slightly lower frequency relevant to sound sourcelocalization, e.g. 1000 Hz, 960 Hz, 1040 Hz.

3. Identification, range determination and sound source localizationinformation is transferred centrally by the right and left auditorynerves. A unitary image is constructed about a central zero-point andheard by ‘mind’ wherein it may be consciously attended and the range andsound source localization may be intentionally known.

4. Throughout its length four rows of hair cells are situated on thebasilar membrane, with the following characteristics:

-   -   a. Row 1: This inner row of hair cells is comprised of receptors        which synapse with the auditory nerve to deliver afferent        impulses.    -   b. Rows 2, 3, 4: Actively tune the basilar membrane to yield the        primary band and sidebands relevant to sound source localization        information.    -   c. Row 3: Actively tunes the basilar membrane to yield the        primary, central band relevant to sound source identification        and its range determination.    -   d. Rows 2, 3, 4: Are the outer hair cells innervated by efferent        fibres of the auditory nerve?

5. Sidebands result from wave-interference of the head shape and arecompared centrally with the platonic form of a regular tetrahedron setin an orthogonal position as the geometric frame of reference.

6. Sidebands are the resultant of Doppler-like shifts determined byshape of the head which creates a sound ‘shadow’.

7. While the duplex theory of sound source localization has served wellfor the understanding of two-dimensional horizontal planar space, it isincomplete. The geometry of the vestibular apparatus suggests atetrahedral-octahedral four-dimensional reference frame thataccommodates, in all directions about a precise point, sound sourcerange determination and localization information. A virtual center forprecision space-time located midway between the tympani is proposed andthe orthogonally-placed regular tetrahedron about that center serves asthe virtual template for central comparison and peripheral adjustmentwhereby, no matter what changes in size and shape of the head and bodyover time, the individual maintains a capacity for precision space-timeorientation. As observed in the barn owl, recent studies suggest gatingof instructive error signals to be the mechanism for this. (MarciaBarinaga: “Sight, Sound Converge in Owl's Mental Map” SCIENCE Vol. 297,30 Aug. 2002, pp. 1462-3 and Yoram Guffreund, Weimin Zheng, Eric I.Knudsen: “Gated Visual Input to the Central Auditory System” SCIENCEVol. 297, 30 Aug. 2002, pp. 1556-9)

Superior Olivary Complex

For approximately fifty years it has been anticipated that the superiorolivary complex of the brainstem, the first brain region innervated bythe two ears, would yield an azimuthal topographic map of auditory spacewhere the neurons are responsive to interaural time difference (ITD).That idea is now open to question and the discovery ofglycine-controlled inhibition raises new possibilities. Congruent withthe tetrahedral theory of sound source localization is the idea of atopographical map of auditory space where the neurons are responsive tointeraural frequency difference (IFD). Thus the functional significanceof glycine-controlled inhibition arising from the medial nucleartrapezoid body innervation (MNTB) may be to maintain a virtualmultispheric concentric topographical map of auditory space relating tosound source localization and relative range determination. In thisinterpretation interaural level difference (ILD) becomes highlysignificant in its determining whether the sound source is to the rightor the left of the organism.

Based on experience with the ‘precision microphone’ and the ‘precisionloudspeaker’ which, taken together, are a working model of the humanhearing system, the virtual topographic map is comprised of a series ofconcentric spheres whereby an event related potential (ERP) is mappedonto that sphere whose radius demonstrates relative range along aproximal-distal axis. The medial olivary complex is challenged byInteraural frequency difference (IFD) which is a product of Doppler-likeshifts in the frequency of an identifier resulting from head shape.Further central processing leads to the potential for consciousidentification of the sound source by humans together with the potentialfor knowing, with intent, both the range and the location of thatsource, while the map of concentric circles may begin to explain theexperience of externalization whereby the sound source is perceived tobe ‘out there’. (George D. Pollak: “Model Hearing” NATURE Vol. 417, May2002 and Antje Brand, Oliver Behrend, Torsten Marquardt, David McAlpineand Benedict Grothe: “Precise Inhibition is Essential for MicrosecondInteraural Time Difference Coding” NATURE Vol. 417, 30 May 2002)

8. A four-dimensional description of reality, where ‘dimension’ isconsidered to simply be a perpendicular to a plane, is essentiallytetrahedral. This lends itself to observer-dependent experience ofspace-time (Minkowski, Einstein), and is the basis of the ‘precisionmicrophone’ which is intended to be essentially biological and,potentially, a key to a deeper understanding of human hearing. As atetrahedron is conceptual and independent of size, its derivative, the‘precision microphone’ is likewise conceptual and independent of size.Ultimately, its deployment at nanoscale may yield new and interestingfacets of the quantum domain.

The ‘precision microphone’ may also be considered a multidimensionalmicrophone gathering information from a multiple, or ‘n’, dimensions. If‘dimension’ means a perpendicular to a plane and if in physical realitya geodesic sphere is simply a polyhedron of high frequency with manyplanes, then a dimension is simply the line connecting the center of oneof the small triangles on the periphery to the center of the sphere, andpassing through the center (zero point) will emerge 180° in the centerof another small triangle. It should not be surprising then, if thatsmall triangle appears to be completely and polarly opposite by itslocation and its 180° rotation from the first. And there may be manydimensions, depending on the frequency of the geodesic sphere. A regulartetrahedron may be considered the polyhedron of least frequency.

Another polyhedron, icosahedron expanded to frequency ‘n’, may elegantlyserve as a computer-generated spherical map of localization and, in thisform, the geometric principles of the ‘precision microphone’ mayultimately serve as a navigational aid.

9. Theoretically, ‘precision microphone’ orthogonally-placed inidentical space-time of a human listener, is expected to yield identicalprimary and sideband information, and if the ‘precision microphone’authentically represents a virtual tetrahedron orthogonally-placed abouta virtual reference point (zero point) located midway between thetympani, its right and left channel information should authenticallyrepresent the identifier together with sound source localization andrange determination information of human hearing.

B. An Approach to Resolving Ambiguities

Comprehensive anticipatory design science (CADS) used in the developmentof the ‘precision microphone’ began by asking: “what is it that wehear?” and then asking: “how does that happen?”, followed by “whatstructures are involved?” and then “what is their shape?” and theprocess moved from the whole to the particular.

To the degree that the tetrahedral theory is complete there is potentialfor understanding and management of ambiguities. For example, because ofthe forward and slightly upward direction of the auditory canal togetherwith the pinna and overlying tragus, no direct sound reaches thetympanum. By design, the tragus pads provide that in the case of the‘precision microphone’, no direct sound reaches the transducer exceptingthrough a narrow horizontal canal which gives the pad a toroidalcharacter. Accessing event related potentials through a very smallaperture significantly limits the so-called ‘cone of confusion’. In thedesign of the ‘precision loudspeaker’, which simultaneously yields tenevent related potentials, there is, also, no direct sound reaching thelistener.

In the human, saccadic movements about the vertical rotational axisfurther resolve ambiguity such that with a slight shift to the left,sound impinging anteriorly on the right of the cone will move further tothe right while sound impinging posteriorly on the right of the zonewill move further to the left.

C. Current Practices

The placing of miniature microphones in the ear canals of livingsubjects or experimental models, e.g. Kemar—“Knowles Electronic Manikinfor Acoustic Research”, probably yields less than authentic informationbecause of unavoidable physical limitations:

“The acoustic environment created by the ear canal and ear drum is onethat 3D sound synthesis strives to simulate. HRTF generation uses smallmicrophones embedded in a real ear canal to help simulate the realacoustic environment. The use of a small microphone in the ear canal canonly approximate the real thing: frequency response is different,position is different, reflection and refraction of sound waves aredifferent”.

D. Selective Auditory Attention

It is hypothesized that:

Row 3 (supra) yields the primary band and encodes the identifier inauditory scene analysis and is available for full conscious attention asit, specifically, is chosen by central filtering mechanisms;

Row 3 yields the primary band and encodes range information which may beintentionally known;

Rows 2, 3, 4 with rows 2 and 4 yielding the secondary bands, are thesound source localization of the identifier in auditory scene analysisand may be intentionally known.

For depiction of primary and secondary bands refer to C. of page 7:Giard et al. Neurophysiological “Mechanisms of Auditory SelectiveAttention in Humans, Frontiers in Bioscience”, v5, d84-94, 1 Jan. 2000

E. Functional Significance of the External Ear

When viewed from the side along the horizontal tilt axis of the head,the external ear appears elliptoid in shape yielding a long axis whichpoints downward at approximately 45 degrees. Its virtual plane tipsforward and downward approximating the virtual plane of the tympanum.The auditory canal, penetrating the structure inwardly, also renders ittoroidal in shape. The tissues of the external ear are comprised of skincovered in part with fine hairs, cartilage which gives thecharacteristic flexible stiffness, and soft tissue comprised of cellswith semi-liquid interiors and bathed in serum. Sound energy perturbsair molecules single-bondedly inter-attracted in maximum flexibility(Willard Gibbs: phase rules). With energetic perturbation, double andtriple bonding of inter-attractive molecules in intracellular and extracellular fluid and cartilaginous solid tissues, respectively,differentiate the effects of sound transmission and attenuation ofexternal ear tissue. Thus the effect on incoming sound energy iscomplex.

F. Auditory Canal

The auditory canal is tilted upwards and forwards and is partiallysheltered by the tragus pad of the outer appendage. Careful examinationof the whole external ear reveals that there is no direct access to thetympanum of sound-related potentials. In ‘precision microphone’ thecentral small-bore horizontal tunnel of the tragus pad does not yielddirect access to the transducer beyond because of the interveningparticulate matter. The external ear canal has an approximate resonantfrequency of 3400 Hz which is thought to be of importance for speechunderstanding. As the cavity medial to the tragus pad is designed to beaperiodic and relatively colourless, it permits a wide-band potentialfor speech understanding.

G. Oval Window and Round Window Niche

It is proposed that there is a functional significance to the oval toround reduction in the outline of the cochlear canal. Through theossicular apparatus of the middle ear, the tympanum connects to the ovalwindow of the inner ear which closes at one end the cochlear perilymphspace which is then closed at its other end by the round window. Thisoval to round reduction through perilymph may parallel the elliptical tocircular enfolding of information by the ‘precision microphone’(multidimensional to unidimensional about a zero-point).

H. The Vestibular Labyrinth

The ‘precision microphone’ is based on a tetrahedral structure andsuggests that we, as humans, are likewise configured, especially inrelation to the vestibular apparatus which, in a single structure,connects our experience of sound, balance and motion. A small step takesus to the suggestion that our central nervous system architecture isoctahedral and one final step suggests that vector equilibrium may bethe architecture of mind and our connection to space-time. Octahedronand vector equilibrium derive step-wise and geometrically from thefundamental tetrahedron.

Our atmosphere attaches to earth and its individual molecules, whilesingle-bonded in their relationships (Gibbs' phase rule), must alsoarticulate in relationship to the surrounding sea of gravity. A simpleconjecture, then, suggests that the complex organ devoted precision-wiseto issues of balance and motion in the field of gravity also relatesprecision-wise to issues of sound transmitted through ahighly-structured medium. If so, it becomes extremely important, then,that the ‘precision microphone’ and its derivative the ‘precisionloudspeaker’ array, relate specifically to the gravitational field. Thisis accomplished by having the long axes of all of the elliptical facesset at 45° to the horizontal.

I. Outer Hair Cells

It is now generally accepted that outer hair cells relate to sensitivityand specificity of the cochlea. It is proposed that the functionalsignificance of three rows of outer hair cells is their encoding notonly of the identifier of an event related potential but also theencoding of simultaneously received information relating to sound sourcelocalization and range determination.

J. Selective Auditory Attention Research

Giard et al. (Giard et al., Frontiers in Bioscience, v5, d84-94, Jan. 1,2000) show on page 7 a graph depicting Primary and Secondary Bands where‘Primary Band’ represents consciously attended information. It isproposed that in the outer hair cells row 3 relates to the identifier inauditory scene analysis and is available for conscious consideration.Range information, received simultaneously, derives from row 3 and canbe known. Rows 2, 3, 4 taken together, relate to sound sourcelocalization and, while yielding information simultaneously received,can be known but is not available for conscious consideration. Rows 2and 4 are probably the generators of secondary band information.

K. Defining Zero Point and Applicability to Assistive Hearing Device

It is conjectured that for humans there is a single horizontal tilt axisarticulating on the occipito-atlantic joint and which passes through thecenters of the oval tympani or slightly higher through the centers ofthe oval windows of the inner ear. An approximate surface location isthe small depression just antero-superior to the tragus on each side ofthe head. For microphone and loudspeakers the axis passes through thecenter of the oval openings and through the center of the structure. Thevertical rotational axis of the head probably intersects the horizontalaxis in the human except, possibly, in some psychopathological states(Feldenkrais-Feldenkrais, M: “Body and Mature Behavior” a Study ofAnxiety, Sex, Gravitation and Learning”, 1949, Madison Conn.,International Universities Press, 163 pp). The intersection ofhorizontal and vertical rotation axes is referred to as zero-pointwhich, in the equilibrious state, is the center of volume of regulartetrahedron. Articulation about a precise zero-point permits accuratedetermination of location of a sound source.

1. ‘Precision microphone’ is separated between the two elements to yieldtwo equal parts that retain the basic ‘twoness’.

2. Parts are attached to subject's head on each side slightly anteriorand superior to the tragus along the horizontal tilt axis of the headand relating to zero point which is the intersection of the horizontaltilt axis with the vertical rotational axis.

3. Parts, while essentially identical in size and shape, are arranged toretain their original or chiral relationship, basic ‘handedness’ ormirror symmetry, namely ½ spin from exact congruence.

4. With the subject standing in the anatomical position with her/hisgaze to the horizon the long axis of each ellipse will be 45° down fromthe horizontal to yield a correct relationship with earth'sgravitational field.

5. By way of amplification right and left signals are transmitted to therespective right and left ear canals via sound insulating ear buds(speakers).

L. Tympanum

On each side the tympanum is oval in outline and its plane tilts bothtowards the center-front and down. It is conjectured that the right andleft planes of the tympani are congruent with planes of a regulartetrahedron set orthogonally with one plane uppermost and horizontal.The ‘precision microphone’ is an abstraction of this and its twoelliptical openings are thought to be congruent with the tympanicplanes.

M. Doppler-Like Frequency Shifting

Reports in the literature (Semple, Malcolm N.: “Auditory perception:Sounds in a Virtual World”, Nature 396, 721-724 (1988) and Kulkarni,Abhjit and Colburn, Steven H.: “Role of Spectral Detail in Sound SourceLocalization”, Nature 396 747-749 (1988) suggest that our ability toexternalize the experience of sound is determined by head-relatedtransfer functions. Our experience is that ‘precision microphone’consistently yields images that are externalized and localizedspherically (720°) when heard over headsets without reference tofiltering (relative boosting, attenuating and delaying of componentfrequencies) of incoming sound waves. Our analyses suggest that theinvariantly proportioned shape of the ‘precision microphone’ yieldsDoppler-like frequency shifting (up and down) that may bealgorithm-managed to produce precision determination of location andrange, and a corollary hypothesis is that the planar congruence oftympanic ellipses with orthogonally-placed (in Earth's gravitationalfield) regular tetrahedral shape is the primary factor in humanexternalization and localization and, that there is also clearcongruence with the planes of the semi-circular canals of the vestibularapparatus.

If these hypotheses hold with robust experimental testing we can expectwidespread application of the principles.

N. Gravitational Field

The gravitational field is the one that becomes understood early inlife, as infants learning to sit up and developing into the humanorganism with its maximum instability coupled to maximum flexibility ofmotion (Feldenkrais, supra). Gravity and its effects are monitored bythe vestibular apparatus which includes the cochlear hearing organrelating to a spherical domain about a central point between the ears.‘Precision microphone’ is a working model of the hearing system in itsrelationship to gravity, The rules of gravity were worked out by Newtonin the seventeenth century.

O. Sound Envelopes

There are three levels of sound envelope, which relate to the structureof the human hearing system:

Level 1 envelope—low frequency sound, undifferentiated as to locationand no reference to a central point.

Level 2 envelope—mid-frequency sound, differentiated as to location on ahorizontal plane (azimuth) about a central or zero point. It gives basicright and left handedness and is the source of inter-aural time andintensity differences that feature in the duplex theory.

Level 3 envelope—high frequency sound, spherically differentiated abouta central point (zero point) that features in the tetrahedral theory.

P. Optimal Shadow

By taking a single orlid (Orlid′ refers to a cylinder cut perpendicularto the axis at one end and truncated at the other end at an angle of 30°16′. Two orlids joined at their cross sections and with the long axes ofboth elliptical openings set at 45′ to the horizontal constitute thebody of ‘precision microphone’ in an orthogonal relationship to thehorizon.) and placing it on a plain white surface with the right angletruncation down and placing it in coherent light such as that from thebright sun and then rotating it, an internal shadow moves in a cyclicfashion yielding a sinusoidal curve. A similar situation prevails whencoherent (natural) sound information falls on the orlid. Anotherapproach is to take the single orlid and wrap a sheet of white paperaround it and then trace out the elliptical outline of the orlid ontothe paper, an externally-derived sinusoidal curve appears. This canreadily be done using a double orlid and the functional significance ofthe dynamics of localization begin to suggest themselves.

The shadow needs to be ‘clean’ and without ambiguity. In the ‘precisionmicrophone’ there is a potential resonant ambiguity produced by thecavity interior to the tragus pad. The cavity can be made relativelyaperiodic by filling the cavity with the lightly oiled fine corkparticles (Gibbs' phase rules relating to solids, liquids, and gases arerelevant to the inclusion of this material.).

Q. Orlid and the Doppler Effect

To demonstrate the Doppler effect of the orlid, embed a singlemicrophone element at the center of the circular end of a cylindricalhorizontal bar. Expose the microphone element to a single tone of knownfrequency. The event related potential will yield a band of similarfrequency. Now cap the bar with an orlid such that the long axis of theelliptical face is 45° to the horizontal and repeat the procedure. Theevent related potential again yields a band of similar frequency(primary band) together with two side bands, one lower and one higher infrequency than the primary band and the frequency relationships of theside bands will vary as the vectorial angle of incidence of the singletone varies. FIGS. 15-16 of Canadian patent 2,076,288, issued Jan. 30,2001, illustrate these effects.

R. Sound Fields are Seamless

Event related potentials taken from a specific space-time location (zeropoint) simply fade away while amplification extends the range. Unlikevisually perceived or felt objects, auditory objects have no boundariesand are manifestations in a seamless universe. An individual's soundfield is a portable, personal and unique abstraction seamlessly derivedfrom a larger whole. And when a recording is made with the ‘precisionmicrophone’, an individual is free to return to a unique location inspace-time to explore again many corners of the sound field with orwithout the psycho-physiological filters accumulated over a lifetime.The listener has central control then, over selective auditoryattention.

S. The Unitary Experience of Listening

“Unity is Plural and a Minimum of Two” (Fuller)

“Two Descriptions Are Better Than One” (Bateson)

It is assumed that in our hearing, information (“Difference That Makes aDifference”—Bateson) at the left ear is different than that at the rightear and, initiated by Lord Rayleigh, this has been the basis forresearch respecting sound source localization over the past 100 years.The language has been that of head related transfer functions or HRTF'Sderived from interaural time and intensity differences.

But, our experience is unitary, that is, we hear single auditoryobjects, not single objects twice as might be expected, and is sometimesthe case in stereophonic representation of events. (There is the case,however, of the person having experienced a catastrophic brainstemlesion who does have ‘stereo’ hearing with sound on the left and soundon the right without the unitary experience.) Unlike stereo, the‘precision microphone’ gives a unitary experience if the associativeneural pathways are intact.

Also, because the ‘precision loudspeaker’ has a parallel associativenetwork, it yields a unitary image that fills all space with no apparentdead spots, and, as is the case with listening in a real sound field,there is an integrity of the relationship between the listener and theimage. As the listener moves about there may be the uncanny sense of animage unwilling to let go.

The simultaneous encoding of not only the identifier but also soundsource localization and range determination information about a specificzero point, the image, as heard over a headset, is akin to beingsurrounded ‘out there’ with the externalization of the experience and,as well, giving a sense of being ‘in-the-sound’.

When program material from the ‘precision microphone’ is delivered asten separate event related potentials by the ‘precision loudspeaker’, anidentical image is reconstructed about the zero point of the loudspeakerarray such that the listener, sitting behind and sharing a right-leftorientation, may find himself or herself literally “in the sound”.

T. Proposed Definitions

When an individual listens, what is it that hears?

Epistemological issues deriving from polarized perspectives such asmaterial realism, on the one hand, and monistic idealism, on the other,sooner or later come into play when we begin to consider the physics ofsubjective experience. It is likely that tetrahedral theory willinterest scientists and philosophers across the epistemologicalspectrum. Consider, then, it reasonable to set out definitions that maybe tentative but have heuristic value. (Goswami, Amit: “The Self-AwareUniverse: How Consciousness Creates the Material World”, 1993, New York,Penguin Putnam Inc. 274 pp.)

“SOUND EXPERIENCES” are mental phenomena that relate directly tophysical events, sound field recordings made with the ‘precisionmicrophone’ and heard over headset, memories, imaginations, dreams,hallucinations, mystical experiences, etc.

“EVENT RELATED POTENTIALS” are perturbations in the atmosphere,vibrations of the ossicular apparatus of the middle ear, evokedotoacoustic emissions, acoustic nerve depolarizations andrepolarizations, related brain activities, etc.

While specific embodiments of the invention have been described in theforegoing, it is to be understood that other embodiments are possiblewithout departing from the spirit and scope of the invention. Thus, forexample the air impervious membranes of the tragus pads may be a singleimpervious envelope, for example a paraffin wax coating or theequivalent. In addition, while external, eyeglass mounted and in-the-earembodiments of the hearing aid application are disclosed, the inventionis readily adapted to other forms of hearing aid, including thebehind-the-ear format.

1. A microphone comprising: a hollow cylindrical housing with a lateralaxis, and having two non-parallel elliptical end faces oriented mirrorsymmetrically with respect to a plane perpendicular to the lateral axis;two circular transducer mounting plates extending across the housing,adjacent the respective end faces, substantially perpendicular to thelateral axis; two microphone transducers mounted centrally in respectiveones of the transducer mounting plates for receiving sound from outsidethe transducer mounting plates; end panels of air-pervious materialextending across and closing the respective end faces; two sound dampingtragus pads secured to inner faces of respective ones of the end panels,each tragus pad having an elliptical periphery spaced from the housing.2. A hearing aid comprising: a cylindrical housing with a lateral axisand having non-parallel elliptical end faces orientedmirror-symmetrically with respect to a plane perpendicular to thelateral axis; two microphone transducers mounted in the housing toreceive sound from the respective end faces; a housing mount formounting the housing on an eyeglass frame such that when worn, thelateral axis is substantially horizontal and the elliptical end facesconverge forwardly and downwardly; amplifiers coupled to the respectivemicrophone transducers for receiving transducer signals therefrom;earpieces including respective earphone transducers connected to theamplifiers for receiving amplified transducer signals and converting thesignals into sounds.
 3. A hearing aid comprising: a cylindrical housingwith a lateral axis and an elliptical end face; a microphone transducermounted in the housing to receive sound from the elliptical end face; anamplifier for receiving electrical signals from the microphonetransducer and amplifying the signals; an earphone transducer forreceiving amplified signals from the amplifier and converting theamplified signals into sound waves; an earpiece for mounting the housingon a human ear with the lateral axis substantially horizontal and longaxis of the elliptical end face sloping downwardly to the front.
 4. Ahearing aid according to claim 2 including a circular transducermounting plate extending across the housing, adjacent the elliptical endface, substantially perpendicular to the lateral axis, the microphonetransducer being mounted centrally in the transducer mounting plate forreceiving sound from outside the transducer mounting plate.
 5. A hearingaid according to claim 4 including an end panel of air pervious materialextending across and closing the end face of the housing.
 6. A hearingaid according to claim 5 including a sound damping tragus pad secured toan inner face of the end panel, the tragus pad having an ellipticalperiphery spaced from the housing.
 7. A hearing aid according to claim 6wherein the tragus pad comprises two membranes secured together alongthe elliptical periphery, a stiffening material between the membranes,and a viscous fluid in the space between the membranes.
 8. A hearing aidaccording to claim 7 wherein the tragus pad includes a circular port onthe lateral axis.
 9. A hearing aid according to claim 6 includingparticulate material filling the housing between the transducer mountingplate and the tragus pad.
 10. A hearing aid according to claim 9 whereinthe particulate material is a sound damping material.
 11. A hearing aidaccording to claim 3 including a circular transducer mounting plateextending across the housing, adjacent the elliptical end face,substantially perpendicular to the lateral axis, the microphonetransducer being mounted centrally in the transducer mounting plate forreceiving sound from outside the transducer mounting plate.
 12. Ahearing aid according to claim 11 including an end panel of air perviousmaterial extending across and closing the end face of the housing.
 13. Ahearing aid according to claim 12 including a sound damping tragus padsecured to an inner face of the end panel, the tragus pad having anelliptical periphery spaced from the housing.
 14. A hearing aidaccording to claim 13 wherein the tragus pad comprises two membranessecured together along the elliptical periphery, a stiffening materialbetween the membranes, and a viscous fluid in the space between themembranes.
 15. A hearing aid according to claim 14 wherein the traguspad includes a circular port on the lateral axis.
 16. A hearing aidaccording to claim 13 including particulate material filling the housingbetween the transducer mounting plate and the tragus pad.
 17. A hearingaid according to claim 16 wherein the particulate material is a sounddamping material.
 18. A microphone according to claim 1 wherein thetragus pad comprises two membranes secured together along the ellipticalperiphery, a stiffening material between the membranes, and a viscousfluid in the space between the membranes.
 19. A microphone according toclaim 18 wherein the tragus pad includes a circular port on the lateralaxis.
 20. A microphone according to claim 1 including particulatematerial filling the housing between the transducer mounting plate andthe tragus pad.
 21. A microphone according to claim 20 wherein theparticulate material is a sound damping material.